The present invention relates to methods for thermal treatment of workpieces or components, in particular for producing a soldered joint between a solder material and at least one component or workpiece used as a solder material carrier by melting of the solder material arranged on the solder material carrier, wherein at least one component is heated in a process atmosphere sealed off from the environment. In addition, the invention relates to a device appropriate for carrying out this method.
A method or a device of the aforementioned type is known from DE 29 08 829 C3 which describes a method for performing a hard soldering procedure in an evacuated process chamber, wherein components to be joined together by melting of a hard solder are joined together. During the hard solder procedure a vacuum is formed in the process chamber and heating of the components to be joined together takes place at approximately 600xc2x0 C.
With this known method a subsequent cooling procedure takes place outside the process chamber in a normal environmental atmosphere.
U.S. Pat. No. 5,782,402 describes a method and a device for producing a soldered joint, whereby the device comprises three chambers which are evacuated for performing the method, such that both the heating and cooling procedure take place in a vacuum. Simultaneous loading of the chambers and thus increased conversion are enabled by the chambers sealed off from the environment.
U.S. Pat No. 5,341,978 describes a device for carrying out a soldering procedure which takes place in a nitrogen atmosphere to avoid oxidation of the workpieces, whereby the nitrogen introduced into the chambers is first evaporated in a cavity limited by an inner and an outer wall of the cooling chamber in order to then be conveyed from the cavity limited by the chamber walls to tire inside of the chambers. There it serves as cooling or oxidation protection. The heat released by the cooling method is used at the same time to accelerate heating of the gas.
The object of the present invention is to propose a method or a device, wherein not only heating of a component, in particular for melting, the solder material, but also cooling of the component in a defined process atmosphere take place, without the heating procedure and the cooling procedure impairing each other.
In the method according to the present invention cooling of the component takes place in a procedural step following on from the heating step in a process atmosphere sealed off from the environment, whereby heating of the component or melting of the solder material and cooling of the component takes place in process chambers independent of one another.
The method according to the present invention basically lends itself for use generally for temperature application to workpieces or components for thermal treatment, such as tempering, annealing and the like, for example. A particular area of application is the production of soldered joints which can be designed both as hard soldered joint and as soft soldered joint, such as for example in the manufacture of electronic components and assemblies.
With the manufacture of soldered joints in particular the method according to the present invention enables not only a cooling procedure controlled similarly to the melting procedure without the procedures mutually influencing one another, but also effective execution of the soldering procedure including the cooling procedure based on the process chambers specified with respect to their task in each case. Reciprocal influencing of both procedures is opposed by the possibility of the formation of different process atmospheres in the various process chambers. In addition, an overall higher quality of the soldered joint results from the cooling carried out in a defined process atmosphere. This proves to be particularly advantageous whenever the soldered joint has not only mechanical connecting functions, as with the connection between metallic components, but also an electrical connecting function, such as for example in the case of boards fitted with electronic components in the SMD (surface-mounted device) method and which are connected by way of a soldered joint mechanically and electrically conductively to the strip conductors of the boards.
With use of the method according to the present invention for mechanically connecting metallic components by means of a soldered joint in particular it proves to be advantageous if in a procedural step preceding melting of the solder material the solder material carrier is prepared by application with a reducing or inert process atmosphere and/or by radiation or with materials in a separate process chamber. This makes it possible, without impairing a process atmosphere particularly suitable for the subsequent melting procedure, to prepare the solder material carrier, for example the metallic components. For this purpose it may be possible to introduce a reduction agent, such as formic acid or the like, into the process chamber, or also to generate a reducing gas atmosphere in the process chamber, whereby before the solder material carrier or the components to be joined together are transferred to the subsequent process chamber for performing the melting procedure the process chamber can be rinsed to counteract any influence of the process atmosphere which has formed in the subsequent process chamber. Such preparation of the solder material carriers or of the components to be joined together can also be effected by plasma application of the components or of the contact surfaces to be moistened with the solder material in the subsequent melting procedure.
A further possibility of counteracting reciprocal influence of the various process atmospheres which have formed in the various process chambers, consists of establishing a vacuum in the respective process atmospheres or the process chambers.
There is also the possibility of creating the process atmosphere in each process chamber as a protective gas atmosphere.
The simplest possible method for adjusting the temperature of the component is feasible if the temperature application occurs by means of a tempering device which is operated to heat or cool the component with a substantially constant temperature. This altogether enables short processing times, because heating or cooling tunes of the tempering device do not apply with continuous operation of the tempering device. For shortening the tempering period or for increasing the tempering rate it has proven advantageous if the temperature of the tempering device is selected clearly higher than the desired processing or soldering temperature.
The simplest possible method for adjusting the temperature of the solder material and/or of the solder material carrier when a soldered joint is being produced is likewise enabled by such a temperature application.
An advantageous form of regulating is enabled if the tempering device is operated as a radiator device, and the temperature of the component or of the solder material carrier is adjusted over the distance of the radiator device from the component or from the solder material carrier.
If the radiator device is combined with a contact device and temperature application occurs at least in one starting phase of the heating or cooling by means of conveying heat or cold, then it is possible to considerably shorten, the heating or cooling periods.
The device according to the present invention for carrying out the abovementioned method has a heating chamber or a melt chamber, in which heating of the component takes place, in particular for melting a solder material for producing a soldered joint arranged on a component serving as solder material carrier, and a cooling chamber for cooling the component attached to the melt chamber, whereby the heating chamber or the melt chamber and the cooling chamber form process chambers independent of one another.
For preparing the solder material carrier for the soldered joint a preparation chamber, which forms a process chamber independent of the melt chamber, can be arranged in front of the melt chamber.
If the process chambers are designed as separate modular units, which can be connected to one another via door mechanisms, the device according to the present: invention can easily be adapted in construction to various methods, so that for example in one particular case the device can be constructed only from a melt chamber and a cooling chamber as required, and in another case by a preparation chamber, a melt chamber to and a cooling chamber, whereby at least partially identical modular units can be utilized to construct the respective device.
It is also possible to build up the process chambers in a modular fashion, in such a way that the door mechanisms are designed as door modules and can be combined with chamber modules to construct the process chambers.
For temperature application of the component arranged on a carrier device in the process chambers formed by the melt chamber or the cooling chamber it is an advantage to provide a radiator device which can be altered in its distance relative to the carrier device or the component by means of a distance alteration device. A temperature application device so designed enables the radiator device to be operated at an essentially constant temperature, whereby the distance of the radiator device relative to the carrier device can be altered to make a change to the temperature of the carrier device heated by the radiator device.
In the need to accelerate heating of the carrier device and thus overall to shorten the sojourn time of the solder material carriers necessary for carrying out the melting in the melt chamber or the instances of cooling in the cooling chamber, it has also proven advantageous to provide the radiator device with a contact device which also enables temperature transmission via heat conduction, apart from temperature transmission via radiation. With use of the radiator device for cooling the component or the solder material carrier the radiator device can be combined with a convection device to improve cooling efficiency.
The simplest possible design of the radiator device with simultaneous formation of a contact device is feasible if the radiator device is designed as a temperable plate, whose surface serves as contact device.
To regulate the distance of the radiator device from the carrier device depending on a desired temperature of the carrier device it proves advantageous to provide the carrier device or the solder material carrier with a temperature sensor, whose output signal serves to define a correcting variable for altering the distance of the radiator device relative to the carrier device. The temperature sensor, which serves to determine the temperature of the carrier device, can also be arranged directly on the radiator device, thus for example on the plate, whereby a touch contact with the carrier device can be guaranteed by a connecting device compensating the modified distance between the plate and the carrier device, such as for example a spring device, independently of the respective distance between the plate and the carrier.
In particular, when the method according to the present invention is designed as a continuous process, wherein the solder material carriers arranged on the carrier device are guided through the subsequently arranged process chambers in a clocked manner while specific sojourn tines in the individual process chambers are adhered to, it has proven advantageous to fit the carrier devices with an information medium which cooperates with a reader device, such that after a carrier device enters a first process chamber the process running in the first and subsequently arranged process chambers is controlled by the information contained on the information medium.
A particularly economical application of the device is feasible if the device comprising at least one heating chamber and a cooling chamber is integrated into a working or manufacturing line as part device in an in line arrangement. When the device for producing SMD boards is used a mounting device for mounting the SMD boards can be connected to the device, for example.
A preferred variant of the method according to the present invention as well as an exemplary device are explained in greater detail hereinbelow with reference to the drawings.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.